Method of making ni3al



Jul 17, 1956 P. P. TURNER, JR., ET-AL SOLUTION 0 o IOO u I: m g 1300 I: s 5 I275 I I E I00 Ni Ni+A| Ni Al n1 SOLID NL SOLID N13 SOLUTION m; m SOLUTION 15 o I D0 .5 I00 WElGHT PERCENTAGE NICKEL YE 771's TE Percy Z? Turner (/1? z 2 euu's c/T Jones w w E: H I H .ZZHE

United States Patent land, Ohio, assignors to Thompson Products, Inc.,

Cleveland, Ohio, a corporation of Ohio Application May 6, 1952, Serial No. 286,418

8 Claims. (Cl. 75-224) The present invention deals with a preparation of improved metallic compositions of good oxidation resistance and having a high degree of workability.

The compositions of the present invention include what may be termed intermetallic compounds in the sense that the predominating ingredient in the compositions represents a combination of two metals in definite molecular proportions. The empirical formula for the preferred compound of. the present invention is NiaAl. We have found that this compound has extraordinary oxidation resistance properties, and excellent hot strength properties, as well as being workable.

In order to understand the structure of the compositions of the present invention, some discussion should be made of theory of solid solutions and the various types of combinations which two or more metals may undergo when combined in the form of a solid solution. It has long been established that in many alloy systems, the addition of one metal to another does not produce a new phase, but results in the formation of a homogeneous alloy which is the result of a solid solution of one metal in the other. The solid solutions which form the end phases in equilibrium diagrams are called primary solid solutions having the samestructure as the parent metal from which the solid solution is formed. Under conditions of solid solution, two distinct types of solid solutions are possible. The first of these, the more general case, is that of a substitutional solid solution in which i the solute. atoms replace those of the solid, so that the two diflerent atoms are situated on a common lattice. The other type of solid solution is the interstitial solid solution in which the solute atoms fit into the spaces between those of the solvent. This latter case occurs when there is a great difference in size between the atoms making up the solid solution, and occurs most frequently when small atoms such as carbon, nitrogen, boron, and hydrogen are combined with metal atoms having a substantially larger size. Ferrite, austenite, and the hard metal carbides, are good examples of interstitial solid solutions.

As the size of the atoms making up the solid solution becomes more nearly equal, a substitutional solid solution results. In most substitutional solid solutions, the different atoms are arranged at random on a common lattice, butin some cases, alloys which at high temperatures consist of random substitutional solutions undergo an atomic rearrangement upon slow cooling or annealing, resulting in the different atoms taking up regular positions in the crystal lattice and thus forming an ordered structure. The basic crystalline structure is, however, the structure of theparent solid solution. This type of structure is now known as a superlattice.

The theory of thesuperlattice is closely associated with the. theory of the intermetallic compound. While there .is no, sharp line of distinction between many superlattice structures and intermetallic compounds, two factors generally contribute'toidetermine where two given elements will combinein the form of superlattice structures,

"ice

intermetallic compounds, or ordinary solid solutions.

The first of these is known as the size-factor which is based upon the closest distance of approach of the atoms within the crystal structure of the solute and the solvent. It has been demonstrated that if the atomic diameters of the solvent and solute differ by more than about 15%, the range of solid solution formation is very restricted, whereas if the difference in atomic diameters is below the limit specified, considerable solid solutions may be formed. The other factor which enters into the problem is the electrochemical factor, by which is meant the degree of separation of the two metals under consideration in the electromotive series. In general, the more electronegative the solute, and the more electropositive the solvent, and vice versa, the greater is the tendency for the formation of stable intermediate compounds.

The formation of a superlattice structure is often accompanied by marked changes in the physical and mechanical properties of the alloy, giving rise to the belief that such superlattice structures may be regarded as definite chemical compounds. However, this cannot be considered the general rule, since from more recent work, it appears that the forces holding the atoms together in a superlattice may be of the same nature as those of a simple metal or a random substitutional solid solution. If these-normal metallic linkages are regarded as a type of chemical combination, then the superlattice structures could properly be considered as definite chemical compounds. On the other hand, if the concept of chemical combination is limited to the formation of homopolar or purely ionic compounds, then the superlattice type structures are not, strictly speaking. true chemical compounds.

Because there is no sharp line of demarcation between superlattice structures and intermetallic compounds, the compositions of the present invention will be referred to as intermetallic compounds. The evidence obtained thus far indicates that the compound NisAl has a crystalline structure of ordered face centered cubic lattice. While the size factors are very favorable to the formation of stable solid solutions (nickel has a crystal lattice in which the closest distance of approach of atoms is approximately 2.5 Angstrom units, while in aluminum, the closest distance of approach between atoms is approximately 2.8 Angstrom units) nickel is no. separated by a very substantial degree from aluminum in the elec- I tromotive series. Consequently, the nature of the forces bonding the atoms together in the ordered structure is not capable of precise definition. Whatever the nature of the forces bonding the elements together, we have found that the compound NizAl has very desirable oxidation resistance characteristics, and hot strength properties not possessed by any other combination of these metals, so far as we are aware.

An object of the present invention is to provide an improved oxidation resistant composition including an intermetallic compound of the type represented by the formula NiaAl.

Another object of the present invention is to provide a method for the production of stable, intermetallic compounds produced by diffusing metallic atoms into an intermetallic compound containing aluminum and lower molecular proportions of the metal being diffused therein than is desired in the final intermetallic compound.

Another objetc of the present invention is to provide a method for promoting solid state diifusion between nickel and intermetallic compounds of nickel and aluminum.

Still another object of the present invention is to provide an improved method for producing a compacted, sintered mass consisting essentially of NisAl.

Formation of the compound NiaAl requires special technique because of the very restricted? area of the: peratur ezmagr; be:dropperkto tltersinteriilgtrange'xofifgwfifli nickel-aluminum phase diagram1in=wliich the: co'rnpoundf t r ZSSO F; Eorrexamnle thes lnlfttu rei can' cate exists as a stable phase. Mcrely miiring metallicalumif toozutemperature ofa 2600-?" [;2656? F ,for: I

num and/metallic nickel in vthe proper atomic. proportions-s r aboutfto:'lO mihutes-andithemtlieopow H 0 :zrele'et I andithcn heating. the mixture. to elevated temperatures 51 furnace turnedt-ogiuntrlia temgeratumsmsthe rangerofe does not produce the dcsired intcrmetall'ic. compound; g300 lh;. to22:550"E;is-achievedawhereugmrsthecfumacex because an oxide scum forms on theaaluminum: causing; lsmamtamed temperaturesi lrr the xlas namedclrangeizfon significantamounts of the: a'luminumitobie unavailable-font the: desiredr-ipe 0d: of time: Withmr.

reaction with nickell In the process offthepresent'zirr v V thespr zeferred i sinter g:temperature rm..-th .vention', metallic nickel is reacted with: therintermetallic: 23905" h N u a I compound NiAl under conditions. offlsolidrstatediffusion; I 'piimoda of. time; reqmredsfor: S01ldt andin' the proper SlIOlChlOm'BlIlC"PI'OROFlZlOllSiTtOZ yieldz the'. dllfusronsotfithezadded:n ckel:intoathet-hltAl tozformolshsAli compoundNisAl; *01611'1'3 omthe'a order-50f one.toxthreet'lrours;although;

The compound NiAl is" not essentially oxidation; re;-- N fPI Q F 10 5?fibllfswainbefienltdoyedi sistant, and is too brittle to be usedzas: at: structuralimate:-.- f RB Q- Q 99 E Ee usedL To avordtoxr rial. This compound exists asa body centered cubic: lhfg 116313 l mltg furnacetshouldthavefaa crystal lattice and we. have found. that a. this. structure: l fw gi w yhm hX Et tfl gfimtneon;. can be' transformed itno. the? ordered: face: centerediicubie: q {km- The single drawing submitted?withfithis'applicatiomi'lf 1 P Q FE Ctl reiOfi lustrates a portion of the; nickelealuminurn' phase:- di'as. d" f; 1451113191111 p a gram in which the compound NiAliexists.. Asiseemfizorm Q? -W ff fl v n mg upenathe an inspection'of this diagram; thewareatinawhicli the; 00111-1" t m g mn at r tn u L h pound NisAl and the liquid. exists inJequiIilSriurni is..very The-51111111?qqmpacmd; smteredimassiconslstingies" v l limited. Itwill be noted frorn'thediagramitliat'the'NisAl'e m ql 'xla l i QQQZI SiStance.cliar+--, field extends from the solidus: temperature;:.about';252' actensncs?thusllfwkmglthe mp fi gl y' s aljl for" F., down to roomtemperature; andlis: adjacent.to e1: W EQ fl' fi q f i'fl t tur field of NiAl'plus NiaAl on: the aluminurn side-ofitlie dia bee -3 E1 "i -Q F t av 9%??? that?! the"; 9 gram and the field ofnickel. solid. solution". plus NisA'li P 1 'ff ;,FT?Yl, FE P- e f on the nickel-side of the'dia'grama Since;thes-preserrcerofi m gnrficantilo'ssadue to:;ox1daethe brittle. compound detracts fromrthei-oxidatiom resist?- ance and workability of thefinalcomposi'tibnsgi =is hilil desirable to stay Within the"fi'eld=ofhomogeneousrNi3Al;,. 1 H .t .t or to favor an excess ofnickeliandlform'thezcombinatiorr. of: Pij lP e imi il' pi of the nickel solid solution andNis'A'l; in prerereneetoe-tnee a Mean "a-mnummhlchfim combination of NiAl and (NizAlJ: age: nntfarlaptedtfbrriuse: in: high? temperature:

In essence, the process of. the presentrinventiom 'j' v q i w volves mixing the' compound: NiA'l and) an amount? of? i g' i siggi t z z g r fof ig l gadditional metallic nickel at least sufficient to' yield". the; 5 o a??? o 2i compound: NiaAl, and sinteringthe;resulting;miirtuneeat 0 9. i a'sintering temperature near butnoti substantia'llyiir 8 A an P cess of the solidus temperature offthe1compoundiNi'sA the m l 2kg" f i ffgggg angesmi After sufficient time has elapsed'to permitsolidistatadr gf g matfwariauy mociificatio 1 ndp fusion, we have: found that the resulti'ng mixture:corr-- pp L t" fr f e tains the substantially pure cornpound'Nl'sAl' 'to' tl'iBZGXCIlL I gffl 9 1 sion'of the compound'NiAl: mpresemlmvmuon" The solid state diffusion'reactionrcan: bei-accelerated iiff finely divided particles are'employed" in-th'e.-ini'tialIreat:-ftion. Consequently, we prefer to USG7PaItitJBSLHHVl'iTgZ and? an ad-df-Onal powdred-t a particle size on the order of 32'57n1esh and smalleiz: esmfisinfimfiyi etmmpundyNihAl i /1 can}? Since the compound NiAl' quitebrilfl; it'cam a paetingt sinteri'rrg; the. resulting: miirture at. a" sinter-" verized into an extremely fine state of subdivision; ifigltempemmmiHemama:solidhsfitemperamm,ofetfieicom; particulated mixture of 'NiAl and) metallic nickel. offthew pmmdif ta'sumd-emi mm? fmcausefl: solidi state, particle size. indicated is'compacte'd from: a fwto-SO' dififisimanditfi fonmafi'mof; isaidfiml-xtureg tons per' square inch, depending on the" density" to? be, 213" mm memnd mepmngjtfiev ihtermtanir achieved. Thecompact is thenheatedTir'r. alii'gli'tempera 901mm w w I p ature furnace. The proportionzzof/nickel: a'ddedt'fis: sub=-- stantially equivalent to" the: stoichiometric'.' amount? off? nickel required to produce the. compourrdl from" the existing NiAl. The.resulting:compositionwillfthereafore have an aluminum concentration of about"13i5%-- p by weight, with the balance being substantially nickell. Cause: 80H 7 State: difmsfiml flies farmatiom my w As previously mentioned; the Presence of Ni'Al" iintlie: cflmpoundfrifizsaiagmimmwv final product is not desirable, so that-.in order' to insure: THEE memode prepafihgz flies aompom r complete'reaction, it isdesirable tovprovide ai' slight: fiifl ig m1 j d amilg msumi-mlr ce of nickel e h h o y quired-10mm amounteofi govvdercdi nick m substantially; duce the compound NiaAli-v The: resulting composition e: metliod of preparing-1: the: intermeta'llict povw dere veons:pound";Nix. ifiteompri'sesvmiirihggtlfeecom W I stoiehiornetriefgortionsssufliefentztoi yielditlieecomgnundt should, however, contaln an alummum-concentration":of- Nigel; ompacting; tli esultingz miirturm. andi sunnin 13.5% by Weight, plus or minus l%',.oir'ot-herwisertli'ei {Hg rgsfllflhggggyugggt mmnmemdflizingamospfibmfauw compound NisAl does not-result: sinteri rrg ttemperat mtliezrangeafmrmmt) mafia In order to-furtherhasten the: diffusion of? tlie a'd'ded? ferra't-sufiicient tnneetoasolidfstat difiusiomandnickel into the NiAl; themixturet can: beaheated'iabove: t formation?ofltliercomnoundi NisAliihiz-saidtmi'xturef. the melting point of nickel initially and then the temi- 41% method off preparing; the; inter-metallic pound NiaAl which comprises mixing powdered NiAl of a particle size not in excess of about 325 mesh and a sum- 'cienl amount of powdered lx'ckel of a particle size not in excess of 325 mesh in substantially stoic-biometric proportions to yield the compound Nix/\l, compacting the resulting mixture, and sintcring the resulting compact in anon-oxidizing atmosphere at a sintering temperature in the range from 2300 to 2550 F. for a sufficient time to cause solid state difiusion and the formation of the compound NisAl in said mixture.

5. The method of preparing the compound NiaAl which comprises mixing powdered NiAl and a sufficient amount of additional powdered nickel in substantially stoichiometric proportions to yield the compound NiaAl, compacting said mixture, heating the resulting compact to a temperature slightly higher than the melting point of nickel, reducing the temperature to a value below the melting point of nickel and in the range from 2300 to 2550 F., and holding said mixture within said range for a period of time silficient to cause diffusion of nickel into said NiAl and recovering a sintered compact consisting essentially of NiaAl.

6. The method of preparing the compound NisAl which comprises mixing powdered NiAl and a sufficient amount of additional powdered nickel in substantially stoichiometric proportions to yield the compound NiaAl, compacting the resulting mixture, heating the resulting compact to a temperature in the range from 2600 to 2650 F., reducing the temperature to a value in the range from 2300 to 2550 F., and holding said mixture at a temperature within said last named range for a period of time sufficient to cause diffusion of nickel into said NiAl and recovering a sintered compact consisting essentially of NiaAl.

7. The method of preparing the compound NiaAl which comprises mixing NiAl and a sufficient amount of additional nickel in proportions sufficient to yield the compound NiaAl, compacting the resulting mixture, and sini tcring the resulting compact i a non-oxidizing atmosphere at a sintcriug temperature in the range from about 2300 to 2400" l". for a HlllllLlCill time to cause solid state diffusion and the formation of Nix/\l in said compact.

References Cited in the file of this patent UNITED STATES PATENTS 1,728,909

Schroter Sept. 17, 1929 1,974,173 Calkins Nov. 13, 1930 2,294,404 Hensel et al. Sept. 1, 1942 2,41l,073 Whitney Nov. 12, 1946 OTHER REFERENCES Alexander et al.: The Nickel Aluminum System," Journal of the Institute of Metals, vol. 6i, No. 2, 1937, pp. 247-263.

Bradley et al.: An X-ray Analysis of the Nickel- Aluminum System, Proceedings of the Royal Society of London, Series A, vol. 159, pages 56-72. particularly page 59.

Floyd: Treatise in Journal of Institute of Metals, vol.

r 80, Bulletin, vol. 1, September 195l-August 1952, pages 

1. THE METHOD OF PREPARING THE INTERMETALLIC POWDERED COMPOUND NI3AL WHICH COMPRISES MIXING THE COMPOUND NIAL AND AN AMOUNT OF ADDITIONAL POWDERED NICKEL SUFFICIENT TO YIELD THE COMPOUND NI3AL, AND COMPACTING AND SINTERING THE RESULTING MIXTURE AT A SINTERING TEMPERATURE NEAR THE SOLIDUS TEMPERATURE OF THE COMPOUND NI3AL FOR A SUFFICIENT TIME TO CAUSE SOLID STATE DIFFUSION AND THE FORMATION OF NI3AL IN SAID MIXTURE. 